In optical transmission systems, optical switches for changing optical paths to achieve switching of an optical signal are being used in recent years. Especially, the matrix type optical switch for changing optical paths between a plurality of inputs and a plurality of outputs is highly demanded. As a typical matrix type optical switch, there is known an optical switch that switches optical paths by putting a micro mirror constructed by the MEMS (Micro Electro Mechanical Systems) technique into and out of a groove provided between optical paths.
FIGS. 1A and 1B show a configuration of the conventional matrix type optical switch. The matrix type optical switch is such that mutually parallel m-optical waveguides (m: the number of inputs) and mutually parallel n-optical waveguides (n: the number of outputs) are crossed, grooves are formed at intersection positions, respectively, and a core of each pair of intersecting optical waveguides is cut away. FIG. 1A is a top view showing the enlarged groove and neighborhood. A groove 53 is provided at an intersection of two optical waveguides 51, 52 each composed of the core layer and the cladding layers.
FIG. 1B is a sectional view taken along line 1B—1B of FIG. 1A. A lower cladding layer 56 and a core layer 57 that will constitute the optical waveguide are deposited successively on a substrate 55, and the optical waveguides 51, 52 are formed by a photolithographic method. The lower cladding layer 56 and the core layer 57 are covered with an upper cladding layer 58 to complete the optical waveguides. The groove 53 is provided by removing the upper cladding layer 58, the core layer 57 and a part of the lower cladding layer 56.
Above the groove 53, a cantilever 59 on whose point an insert plate 54 is mounted is installed. The cantilever 59 with the insert plate 54 is configured so that the insert plate 54 is movable in a depth direction of the groove 53, i.e., in a direction perpendicular to the optical waveguides. When the insert plate 54 does not block the core layer 57, the optical waveguides 51, 52 will be in a transmission state; when the insert plate 54 blocks the core layer 57, the optical waveguides 51, 52 will be in an interception state. In the interception state, since the insert plate 54 has a reflecting surface 4, light inputted from the optical waveguide 51a can be coupled to the optical waveguide 52a, and light inputted from the optical waveguides 51b can be coupled to the optical waveguide 52b. Thus, an m×n matrix type optical switch can be constructed.
A relative position of the insert plate 54 to the groove 53 is controlled by driving the cantilever 59. As one of typical driving principles, the control is performed by temperature control with a bimetal. For example, electrical wiring serving as a resistive heat generating source is provided on the cantilever 59, its temperature is controlled by changing an impressed current therein, and a position of the insert plate 54 is adjusted by means of balance between a driving force by the bimetal and a repulsion force of a spring fixed to the cantilever 19. Moreover, a method whereby a free point part of a cantilever is drawn up to a fixed substrate side with an attractive force of static electricity is described in M. Katayama et al. “Micromachined 2×2 Optical Switch Array by Stress-Induced Bending,” Technical Digest of Fourth International Topical Meeting on Contemporary Photonic Technologies (CTP 2001), p. 27–28, Mc-4, Jan. 15–17, 2001.
In the conventional driving principle, an impressed current for heating the bimetal and an applied voltage that defines the amount of static electricity given against the repulsion force are controlled in order to control the repulsion force of the spring of the cantilever. This principle has, however, a problem that this scheme cannot detect a relative position of the insert plate to the groove and acquire information necessary to determine a static position.
Therefore, there is also a problem that the principle cannot detect secular change of the relative position of the insert plate to the groove that is caused by variation in a mechanical characteristic of the cantilever as a bimetal, deformation of a supporting joint part between the insert plate and the cantilever, etc., and therefore malfunction of the insert plate caused by breakage of the cantilever etc. also cannot be detected.